Additive containing n-(n-butyl)thiophosphoric triamide for urea-based fertilizer

ABSTRACT

A dry flowable additive for aqueous urea-based fertilizers made of solid urea formaldehyde polymer (UFP), N-(n-butyl) thiophosphoric triamide (NBPT), and, optionally, dicyandiamide (DCD), wherein the liquid fertilizer containing the additive provides reduced nitrogen loss from the soil. Optionally, the dry additive may also be blended with molten or solid urea to form a solid urea-based fertilizer with reduced nitrogen loss from the soil.

FIELD OF THE INVENTION

The field of the invention is urea-containing fertilizers. Morespecifically, this invention discloses a dry, flowable additivecontaining N-(n-butyl) thiophosphoric triamide (NBPT), solidurea-formaldehyde polymer (UFP), and, optionally, dicyandiamide (DCD)which can be combined with a urea-based fertilizer to prepare afertilizer which provides reduced nitrogen loss from the soil.

BACKGROUND OF THE INVENTION

Nitrogen is an important plant nutrient. In addition to phosphorous,potassium, and other nutrients, nitrogen is needed to support the growthand development of plant life. Some plants, such as legumes, through asymbiotic relationship with Rhizobium bacteria, fix elemental nitrogenfrom the atmosphere and fix this nitrogen into the soil. However, mostplants grown to produce human and animal food require the use ofnitrogen fertilizer in order to sustain their agricultural production.

The most widely used and agriculturally important high-analysis nitrogenfertilizer is urea, CO(NH₂)₂. While most of the urea currently producedis used as a fertilizer in its granular form, urea-based fluidfertilizers are also well known. As used herein, the term “fluidfertilizers” encompasses liquid fertilizers, i.e. aqueous solutions offertilizers, and suspension fertilizers, i.e. fertilizer compositionswhich in addition to water and water-soluble components also containinsoluble components kept in suspension by a suspending agent, such asclay. Suspension fertilizers are excellent carriers for pesticides andmicronutrients.

The most commonly known urea-based liquid fertilizer is an aqueoussolution of urea and ammonium nitrate, referred to in the fertilizertrade as UAN solution. These fluid fertilizers are used on a variety ofcrops, such as corn and wheat. When applied to moist soil, the ureacomponent of the fluid fertilizer becomes a source of ammonia as aresult of hydrolysis catalyzed by urease, an enzyme produced by numerousfungi and bacteria. The process is fully disclosed in U.S. Pat. No.5,364,438, which is hereby incorporated by reference. Unfortunately, theurease-catalyzed hydrolysis often converts the urea to ammonia morequickly than it can be absorbed by the soil, resulting in undesirableammonia loss to the atmosphere through a process called volatilization.

Urease inhibitors slow down the conversion of urea to ammonia, extendingthe period of nitrogen release. One urease inhibitor is N-(n-butyl)thiophosphoric triamide (NBPT). When incorporated into a urea-basedfertilizer, NBPT reduces the rate at which urea is hydrolyzed toammonia. This allows the nutrient nitrogen to be available to the soiland plants over a longer period of time. NBPT is widely recognized as aneffective urease inhibitor, but NBPT is notoriously difficult to handle,because industrial grade NBPT is a waxy, sticky, heat-sensitive andwater-sensitive material. As a result, a solvent system was disclosed inU.S. Pat. No. 5,364,438, that allowed the solution of NBPT to be appliedto UAN. However, this solution had stability problems as well asproblems in delivering and metering into fluid fertilizer.

U.S. Pat. No. 5,352,265, which is hereby incorporated by reference,discloses a granular fertilizer comprising about 90 to 99% urea, 0.02 to0.5% NBPT and about 0 to 2.2% DCD. The NBPT is added to molten urea as aconcentrated solution in an amide solvent. The DCD is added to the ureamelt as a solid. This granular product is made to apply directly to thefield crop.

The present invention of a dry flowable additive, is prepared by coatinga solid urea-formaldehyde polymer (UFP) with a solution or suspension ofNBPT in a liquid solvent, preferably an amide solvent. Optionally, thecoated UFP may be blended with solid DCD. Prior to application of thefertilizer to the field crop, the dry flowable additive is blended witha UAN solution or aqueous urea, to form the fluid urea-containingfertilizer composition, or blended with solid or molten urea to form asolid urea-based fertilizer. The present invention provides a fluid orsolid fertilizer composition that is easy to handle and stable whenstored.

SUMMARY OF THE INVENTION

All percentages are by weight, unless otherwise indicated. The presentinvention is a fluid fertilizer composition, comprising an aqueoussolution of UAN or urea, NBPT and, optionally, DCD. A dry flowableadditive for the UAN or aqueous urea is prepared by coating a solid UFPwith a solution or suspension of NBPT in a liquid solvent. The NBPT ispresent in the dry additive in the amount of about 0.40 to 15.0%. Thesolid UFP is present in the range of about 3.0 to 15.0%. Optionally,solid DCD can be blended with this coated UFP in the range of 40.0 to95.0%, and silicon dioxide in the range of from about 0 to 3%. Prior toapplying the UAN or urea, the dry additive is blended with aqueous UANor urea in the range of about 0.4 to 2.5% additive to form the fluidurea-containing fertilizer composition. Alternatively, the dry flowableadditive may also be added to molten urea or solid urea and granulatedto provide a dry fertilizer. The composition of the present inventionmay be applied to a field crop to minimize the undesired loss of ammonianitrogen from surface-applied urea and nitrogen loss in the soil due toleaching and denitrification of nitrate nitrogen.

DETAILED DESCRIPTION OF THE INVENTION

The term NBPT as used throughout this specification refers not only toN-(n-butyl) thiophosphoric triamide in its pure form, but also toindustrial grades or other grades of the material which may contain upto 50% impurities. The preferred NBPT is at least 50% pure, the mostpreferred NBPT is greater than 50% pure, in the range of about 51 to 90%pure. The NBPT is present in the dry flowable additive in the range ofabout 0.4 to 15.0%.

A NBPT solution or suspension in an amide solvent, such as N-alkyl2-pyrrolidone, is used to prepare the dry flowable additive of thepresent invention. The solution or suspension contains between about 30%and about 80% NBPT, and preferably between about 50% and about 75% NBPT.The NBPT solution may be prepared by dissolving or suspending NBPT in asolvent selected from a group of liquid amides such as an N-alkyl2-pyrrolidone, or by adding the N-alkyl 2-pyrrolidone into the NBPTproduction system in order to produce an NBPT solution, rather thanrecover a waxy NBPT solid. Alternatively, molten NBPT, withoutadditional solvents, may be used to coat the UFP in the presentinvention.

The solid UFP of the present invention is preferably a polymethyl urearesin with approximately 0.6% reactive methylol groups. It has primaryparticles of 0.1 to 0.15 μm, forming agglomerates of 3.5 to 6.5 μmdiameter on average. The preferred solid UFP is marketed as PERGOPAK M®2, a trademark of Albemarle Corporation. The solid UFP is present in thedry flowable additive in the range of about 3 to 15%. The most preferredsolid UFP is PERGOPAK M® 2 product or the unrefined pre-cursor toPERGOPAK M® 2.

The optional DCD of the present invention has preferably a particlerange from about 50 to 350 μm. The DCD is present in the dry flowableadditive in the range of about 40 to 95%. In a further embodiment of theinvention, the dry flowable additive may contain from about 1.0 to 30.0%solid UFP and from about 99.0 to 70.0% DCD.

The balance of the composition consists primarily of water, and anN-alkyl pyrrolidone may also be present in small quantities. Thecomposition may optionally also contain a suspending agent, such asclay, as well as other additives, such as a herbicide, a dye, an NBPTstabilizer, or a micronutrient. Silicon dioxide, a flow agent, isoptionally present in an amount of up to about 3% of the dry flowableadditive.

The dry, flowable additive prepared without the optional DCD containsabout 1 to 80% NBPT and about 99 to 20% solid UFP.

The dry flowable additive is added to the UAN solution, aqueous urea, orsolid or molten urea, in the range of about 0.1 to 5.0% additive in thefinal product. Preferably, the dry flowable additive is added in therange of about 0.4 to 2.5% to fluid UAN or urea solution, or blendsthereof, to form a fluid fertilizer. The fluid urea-based fertilizer ofthe present invention contains from about 0.004 to 1.50% NBPT, fromabout 0.040 to 0.850% DCD, from about 0.030 to about 0.30% UFP, and fromabout 99.9 to 98.0% aqueous UAN. Optionally, the fertilizer can containup to about 0.03% silicon dioxide. The aqueous UAN contains urea andammonium nitrate in concentration ranges of about 15 to 50%. A preferredrange is from about 25 to 40%.

The UAN-based fluid fertilizer composition of this invention can be usedin all agricultural applications in which UAN is currently used. Theseapplications include a very wide range of crop and turf species, tillagesystems, and fertilizer placement methods.

The following example is to illustrate the invention and is not presentto limit the invention or claims in any manner.

EXAMPLE

The Example is a laboratory preparation of a dry flowable additivecomposition.

200 grams of 50% NBPT solution in N-alkyl 2-pyrrolidone was added to73.4 grams of solid UFP (PERGOPAK M® 2) and 0.5 grams of a blue dye (FD& C blue #1). The mixture was blended until a uniform mix was achievedas indicated by the distribution of the blue color. This mixture wasblended with 1270 grams DCD and further blended to a uniform color toform the dry flowable additive.

TABLE 1 Composition of Example 1 Component Mass (g) % Component 50% NBPTsolution 200.0 12.95 (6.47% NBPT) Solid UFP 73.4 4.75 Blue dye 0.50 0.03DCD 1270.0 82.27 Total 1543.9 100.0

The dry flowable additive prepared in Example 1 was mixed with aqueousUAN to form a fluid urea-based fertilizer and tested for efficacy as aninhibitor of ammonia volatilization using test methods known to thoseskilled in the art of volatilization testing. A control sample did notcontain NBPT, and the three samples of the invention had NBPT at levelsof 0.013%, 0.026% and 0.051% respectively in the final fluid UANfertilizer composition. It was found that the presence of NBPT waseffective in reducing ammonia loss, particularly at the 0.026% and0.051% levels when compared with fluid UAN fertilizer without NBPT (thecontrol).

1.-20. (canceled)
 21. A fertilizer composition comprising: urea; and acomposition comprising: a. N-(n-butyl) thiophosphoric triamide (NBPT) inthe range of about 1 to 80 weight %, and b. solid urea formaldehydepolymer (UFP) in the range of about 99 to 20 weight %, wherein the UFPis a polymethyl urea resin.
 22. The fertilizer composition of claim 21,wherein the fertilizer composition further comprises dicyandiamide(DCD).
 23. The fertilizer composition of claim 21, wherein the urea ismolten urea.
 24. A fertilizer composition comprising: a. N-(n-butyl)thiophosphoric triamide (NBPT) in the range of about 0.004 to 1.5 weight% of the total composition; b. dicyandiamide (DCD) in the range of about0.04 to 0.85 weight % of the total composition; c. silicon dioxide inthe range of about 0 to 0.03 weight % of the total composition; d. solidurea formaldehyde polymer (UFP) in the range of about 0.03 to 0.30weight % of the total composition, wherein the UFP is a polymethyl urearesin; and e. urea ammonium nitrate (UAN) solution aqueous urea, ormixtures thereof, in the range of about 98.0 to 99.9 weight % of thetotal composition.
 25. The fertilizer composition of claim 24, whereinthe urea is UAN.
 26. A method of preparing a fertilizer composition ofclaim 24, wherein the NBPT and solid UFP is mixed with a urea to providea urea-based fertilizer having the following composition: a. NBPT in therange of about 0.004 to 1.5 weight %; b. DCD in the range of about 0.040to 0.85 weight %; c. silicon dioxide in the range of about 0 to 0.03weight %; d. solid UFP in the range of about 0.03 to 0.30 weight %; ande. a urea in the range of about 98 to 99.5 weight %.
 27. The method ofclaim 26, wherein the urea is UAN.
 28. A composition comprisingN-(n-butyl) thiophosphoric triamide (NBPT) in about 1 to 80 weight % andurea formaldehyde polymer (UFP) in about 99 to 20 weight %, wherein theNBPT is a solution or suspension in an amide solvent and the UFP is apolymethyl urea resin.
 29. (canceled)
 30. The composition of claim 28,wherein the composition further comprises a dye product.
 31. Thecomposition of claim 28, further comprising an aqueous urea solution.32. The composition of claim 28, further comprising molten urea.